This invention relates to a process for disposing of low value oligomeric hydrocarbon and producing higher value hydrocarbon products. More particularly, this invention relates to a process for upgrading low value oligomeric hydrocarbon in a fluid catalytic cracking process ("FCC") to produce higher value hydrocarbons, including those useful for the production of fuels.
The commercial production of solid polymers often results in the production of liquid by-product wastes that must be disposed of in the course of doing business. For example, commercial polystyrene plants can often produce minor amounts of a liquid by-product waste stream comprising unpolymerized styrene, dimers, trimers, and low molecular weight oligomers that are not easily consumed internal to the plant. Based on an estimate of about 1% of the total polystyrene produced, this liquid by-product waste from polystyrene plants amounts to more than 200,000 barrels per year of liquid by-product waste that must be landfilled, incinerated, or otherwise disposed of. Moreover, this liquid by-product material is classified by the Environmental Protection Agency as a hazardous waste due to its volatility and flammability and must be disposed of accordingly. The disposal cost, administrative effort, and the complexity involved in managing this waste stream are substantial.
While there has been this long felt need in the chemical industry for a low cost method of disposing of such liquid by-product wastes comprising unpolymerized monomers, dimers, trimers, and low molecular weight oligomers, this need has been neglected and these materials continue to be incinerated or landfilled at alarming rates.
The need to dispose of solid polymeric organic wastes such as plastics and rubber has been recognized and methods for disposing of such solid wastes have been under development for several years. These methods generally require the use of physical, chemical, or thermal means to break down the solid organic waste followed by a thermal or catalytic reaction step to convert the organic waste to higher value products.
The thermal conversion methods generally include a pyrolysis or coking reaction which requires heating a mixture containing the solid organic waste to high temperatures and, in the absence of a catalyst, for thermally cracking the organic waste to lower molecular weight hydrocarbon.
For example, U.S. Pat. No. 4,118,281 to Yan discloses such a process for disposing of solid organic wastes in a coking process. The process comprises slurrying solid organic wastes in hot coker recycle or fresh petroleum feedstocks at temperatures ranging from 300.degree. F. to 1000.degree. F. and coking the feedstock to produce gas, oil, and coke.
U.S. Pat. No. 4,724,068 to Stapp discloses a process for increasing the API gravity of a hydrocarbon feedstream boiling at a temperature in excess of 1000.degree. F. The process comprises contacting the hydrocarbon stream with hydrogen, hydrogen sulfide, and a polymer, which is solid at 25.degree. C. and 1 atmosphere and contains homopolymers and/or copolymers of olefinic monomers. The contacting step is conducted in the absence of any solid, inorganic cracking catalysts or hydroconversion catalysts promoted with metals or compounds of metals.
The catalytic conversion methods generally require heating a mixture comprising the solid organic wastes to high temperatures and contacting the mixture with a catalyst for catalytically converting the organic wastes to lower molecular weight hydrocarbons.
For example, U.S. Pat. No. 4,175,211 to Chen et al. discloses a process for disposing of solid polymeric wastes in an FCC. The process comprises solubilizing rubber and/or plastic solid wastes at high temperatures with a refractory petroleum stream and catalytically cracking the mixture.
U.S. Pat. No. 4,151,216 to Smith discloses a process for converting solid by-product polypropylene to a high viscosity fuel oil suitable for pumping and storage. The process comprises heating the solid by-product polypropylene to a temperature ranging from about 150.degree. C. to about 350.degree. C. to provide a molten feedstock, and contacting the molten feedstock with a silica-on-alumina catalyst containing 5 to 20 percent by weight silica. The process is conducted in a tubular reactor at temperatures ranging from about 425.degree. C. to 475.degree. C.
U.S. Pat. No. 4,108,730 to Chen et al. discloses a process for converting relatively ash-free solid polymeric wastes, such as rubber tires or plastic, to more valuable liquid, solid, and gaseous products in an FCC. The process comprises grinding the polymeric wastes, slurrying the ground wastes in a petroleum-derived stream, heating the slurry to dissolve the polymeric waste, and processing the dissolved wastes in an FCC.
U.S. Pat. No. 4,143,086 to Carle et al. discloses a process for disposing of amorphous polypropylene and titanium catalyst residue in an FCC. The process comprises at least partially dissolving the amorphous polypropylene and titanium catalyst residue in FCC slurry oil through heating and mixing means and processing the composite feedstock in an FCC cracking process. The titanium catalyst residue beneficially deactivates metals present in the FCC process that can poison the catalytic cracking catalyst.
Another process endeavors to combine a thermal cracking step with a catalytic cracking step for converting solid organic waste to higher value hydrocarbon.
U.S. Pat. No. 4,851,601 to Fukuda et al. discloses a process for producing low pour point hydrocarbon. The process comprises thermally cracking molten plastic waste material and contacting the thermally cracked products with an intermediate pore size zeolite, such as ZSM-5, at a temperature of from 200.degree. C. to 340.degree. C. to effect low temperature catalytic cracking of the thermally cracked products.
The above processes have met with marginal technical success and only limited commercial success. The above processes generally require a solid organic waste collection step which requires the processing facility operator to collect such wastes or contract with outside waste collectors. Where the organic wastes comprise plastics, the collected materials are generally an assortment of various plastics and contaminants that can prove detrimental to the thermal or catalytic cracking process. For example, polyvinyl chloride (PVC), a commonly collected plastic, is a particularly undesirable feedstock for an FCC as it can cause equipment fouling and corrosion. Contaminants such as bottle labels and metal caps must also be accommodated.
Once the collection obstacles are overcome, the solid organic waste must be solubilized for injection into the process. This step often requires the addition of liquid solvent streams and high temperatures. In particular, the process requires solids-grinding, solvent-mixing, and high temperature melting steps that are difficult to perform continuously and can require a tedious batch-mixing process. Under even the most ideal of circumstances, complete solubility can not be expected and the process operator risks equipment pluggage, fouling, and costly process downtime.
Where the solubilized organic wastes comprise polystyrene, the polystyrene may be converted to and remain as styrene. Styrene monomer is a known equipment foulant, particularly with regard to heat exchanger and distillation tower internals. If the polystyrene solid organic waste is not fully converted to another chemical form such as ethylbenzene, equipment failure and costly unit downtime are imminent.
Processing solid polymeric organic wastes on an FCC poses costly processing penalties aside from those connected to accumulating and preparing the waste for injection and the deleterious effects of the contaminants. Adding solid polymeric organic wastes such as plastic or rubber to an FCC result in a substantial increase in coke formation on the FCC catalyst. This coke must be burned off of the catalyst in the FCC regenerator resulting in an increase in the regenerator temperature and an increase in the temperature of the catalyst provided from the regenerator to the reaction step. Since most commercial FCCs operate in heat balance and the regenerated FCC catalyst is contacted with the feedstock such that the combined reaction mixture of regenerated catalyst and feed are maintained at a targeted reaction temperature, the ratio of catalyst to oil necessary to meet this reaction temperature target will be reduced. When the catalyst to oil ratio is reduced, overall FCC conversion of higher boiling hydrocarbon to more valuable lower boiling hydrocarbon is reduced, thereby resulting in a substantial downgrade in FCC product value. In short, adding solid polymeric organic wastes to FCC feedstock for processing in an FCC has been shown to increase catalyst coke formation and lower catalyst to oil ratios such that the product slate produced from the FCC is substantially downgraded in value.
For all of the reasons set forth above, chemical plant and refinery operators have avoided the risks attendant to processing solid polymeric organic wastes as set forth hereabove or applying these or similar technologies to liquid by-product wastes and the technology has languished. This is notwithstanding the fact that: (1) most chemical plant and refinery operators already possess much of the capital equipment necessary to process these materials using the methods described above, and (2) landfill costs are exceedingly high and increasing every day.
It has now been found that an entire field of organic wastes comprising unpolymerized monomers, dimers, trimers, low molecular weight oligomers that, to date, have been historically landfilled as a hazardous waste or incinerated, can be catalytically reacted in an FCC to produce higher value hydrocarbon.
It has been found that injection of a feedstock comprising unpolymerized monomers, dimers, trimers, and low molecular weight oligomers, as defined herein, into an FCC does not increase overall FCC catalyst coke make, notwithstanding the fact that extensive research has shown that solid polymeric materials such as plastic and rubber generally increase catalyst coke make in an FCC. Surprisingly, it has been found that the injection of the feedstock contemplated herein actually reduces FCC catalyst coke yield below that of many conventional FCC feedstocks thereby providing a net processing incentive to accommodate such feedstocks.
It has also been found that injection of a feedstock comprising unpolymerized monomers, dimers, trimers, and low molecular weight oligomers, as defined herein, is not compromised by any of the previously identified problems relating to waste collection, sorting, processing, solubility, equipment pluggage, and contamination that have derailed previous attempts to monetize solid polymeric organic wastes.
It is therefore an object of the present invention to provide a safe, efficient, and economic process for monetizing unpolymerized monomers, dimers, trimers, and low molecular weight oligomers that have been historically landfilled or incinerated.
It is another object of the present invention to provide a process for catalytically cracking a feedstock comprising unpolymerized monomers, dimers, trimers, and low molecular weight oligomers that does not increase FCC catalyst coke yield and increases FCC product value.
It is yet another object of the present invention to provide a process for catalytically cracking a feedstock comprising unpolymerized monomers, dimers, trimers, and low molecular weight oligomers that is not compromised by problems relating to waste collection, sorting, processing, solubility, equipment pluggage, and contamination such as those that have discouraged previous attempts to monetize solid polymeric organic wastes.
Other objects appear herein.